Dental composite material for restoring teeth was first introduced into dentistry about the mid 1960's. The initial composites had a paste-like consistency. As a result, dentists encountered considerable difficulty in the placement of such composite material into a prepared tooth. Generally, the dentist would apply such paste-like composite resin material to a tooth by means of a spatula, palate or like tool. This manual technique resulted in the tooth being filled from the outside in. It was noted that this spatula technique of placing such composite resulted in the formation of voids within the finished restoration. This was because the spatula or palate technique of placing such material in a tooth could not satisfactorily pack the paste composite material into the small and difficult to reach areas of the tooth. The placement of such composite material with a palate or spatula also resulted in the entrainment of air and the formation of air bubbles in the composite material as it is being placed. The formation of such voids or air bubbles compromised the strength and durability of the finished restoration. A further difficulty that was encountered by the dentist was that such composite material had a tendency to stick to the palate or spatula, causing the material to be pulled away when the dentist removed the palate or spatula. Also, if a dentist used a metal instrument to place the composite material, there was a tendency of the metallic instrument to react and discolor the composite.
The problems initially encountered by the dentist in placing such composite resins were solved by the development of the syringing technique for the placement of such composite materials. This syringing technique was first disclosed in U.S. Patent 3,581,399 granted June 1, 1971 to Dr. William B. Dragan. The syringing technique and unit dose capsules disclosed in said U.S. Pat. No. 3,581,399 was followed up by other capsule improvements as disclosed in U.S. Pat. Nos. 4,963,093; 4,969,816; 5,083,921; 5,129,825; 5,165,890 and 5,172,807. These known capsule constructions proved satisfactory for placing the composite materials having a paste-like consistency and/or a composite material having a filler content of less than 78% by weight.
Other known capsules from which such paste-like composites could be syringed are disclosed in U.S. Pat. Nos. 4,330,280; 4,384,853; 4,391,590; 4,767,326; 5,100,320; 5,322,440; 5,460,523 and 5,707,234.
Generally, these known capsules are provided with a reservoir portion for containing a predetermined supply of dental material having an internal diameter which is substantially greater than the internal diameter of the discharge orifice. These known capsule constructions have been designed to handle and be used with the then available composites having a paste-like consistency, i.e., a composite resin composition having a filler content of 78% by weight or less. The lower the filler content, the less viscous the material, and the more readily it can be syringed through the relatively small discharge orifice of the known capsule designs.
More recently, the composite dental materials are being formulated with a substantially larger filler content, i.e., more than 78% filled whereby such highly filled or ultra dense composites are rendered "packable" or "condensable" to imitate amalgam in consistency. Such ultra dense or condensable composite materials are particularly suitable for restoring the back or posterior teeth. The particular condensable properties of such ultra dense composite materials makes it difficult to dispense from bulk syringes. The extreme viscous properties of such ultra dense dental composites have also prohibited the placement of such ultra dense composite material by the use of the syringing technique utilizing the known capsule constructions, which the dental profession has virtually universally adopted as the preferred method of delivering a composite material directly into a prepared cavity.